Z-axis(?) Gouging Wood

[boom-shanka]

Hello

I have an issue that seems to be getting worse - but i'm not 100% sure where the problem lies.

Basically the z-axis (i think) is slightly gouging the wood at random intervals - well not so random as if i travel up the Y-axis, zero-Y (say 150mm) & run the job again the gouges are in the same place.



This first (poor quality) photo i started on the right piece - i then made the left piece to troubleshoot the gouging & the problem disappeared. The difference between pieces is the left has more of a curve while the right is more angular (45 deg). Both used a 8mm flat endmill.



Unfortunately the problem now appears on my curved pieces as well as in the picture. This is a 8mm ball endmill.

I have replaced the key pin in the z-axis motor & halved the z-axis acceleration but still issues.

Any ideas where i start looking for problems?

Cheers

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[tgdavies]

Is the z axis `slipping` in some way, or is it going to incorrect positions during the job but keeping its correct position overall?

For instance, after that job, if you zeroed the z-axis was it at the correct position, that is the same zero you started with?

[awerby]

Do you notice any vibration at the tool tip, as the cut progresses? Or is the spindle rock-solid, not deflecting even if you lean on it hard? Cutting wood puts a lot of strain on the machine, which can dig in and release as the grain permits, if the whole assembly isn't rigid enough to discourage that. To me, the marks you circled have the look of harmonic vibration rather than lost steps. If there's anything you can tighten to get more rigidity in your setup, do that.

[routalot]

The problem may be within the software that generated the code,specially if you selected an incremental retract.Could you tell us a bit about the parameters that created the code?Beyond this,what drives the machine?

[boom-shanka]

I'm using Fusion360 to generate the gcode which is loaded with Mach3.
I haven't had any problems before with code generation - as in what (3D model) i put in is what (gcode/mill result) i get out but i'm open to anything.
What exactly is incremental retract? I couldn't find anything in my search results or a Fusion360 analogous setting

[boom-shanka]

Do you notice any vibration at the tool tip, as the cut progresses? Or is the spindle rock-solid, not deflecting even if you lean on it hard? Cutting wood puts a lot of strain on the machine, which can dig in and release as the grain permits, if the whole assembly isn't rigid enough to discourage that. To me, the marks you circled have the look of harmonic vibration rather than lost steps. If there's anything you can tighten to get more rigidity in your setup, do that.

It seems pretty solid - in my basic tests there isn't much movement at all; i haven't tried pushing spindle mount while it's been moving so will try that.

[boom-shanka]

Well i think the problem has been resolved - it seems my feed setting was too high in Fusion360 (7000mm/min); i dropped down to 4000 & problem goes away;

The thing is if i override the feed speed in Mach3 by say 180% (7200) the problem does not occur either, so that's fine by me.

Thank you all for your help

[routalot]

Its good to know the problem has gone away.The incremental retract I mentioned is an option that appears in some CAM programs that retracts the tool in z by a specified amount from the position it is in at the end of a cut and it then travels directly to the feed in height for the next cut.If there is a piece of the job in the way it gets gouged in much the way that your job has.It is always safer to use an absolute retract height,but it may increase the time taken for the sequence to run.The better CAM systems have a feature to check for gouging and its always a good idea to run a simulation,whatever program you run.

[boom-shanka]

Right, i understand thanks. It sounds like a good idea in some cases for speeding jobs up, i'll def look into it - all of my jobs have had an absolute retract in any case.

[UnionTech]

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Whatsapp: +8618615200463
I think he can help you.